The optimum mercury vapor pressure for production of 2537 .ANG. radiation to excite a phosphor coating in a fluorescent lamp is approximately six millitorr, corresponding to a mercury reservoir temperature of approximately 40.degree. C. Conventional tubular fluorescent lamps operate at a power density (typically measured as power input per phosphor area) and in a fixture configuration to ensure operation of the lamp at or about a mercury vapor pressure of six millitorr (typically in a range from approximately four to seven millitorr); that is, the lamp and fixture are designed such that the coolest location, i.e., cold spot, in the fluorescent lamp is approximately 40.degree. C. Compact fluorescent lamps, however, including electrodeless solenoidal electric field (SEF) fluorescent discharge lamps, operate at higher power densities with the cold spot temperature typically exceeding 50.degree. C. As a result, the mercury vapor pressure is higher than the optimum four to seven millitorr range, and the luminous output of the lamp is decreased.
One approach to controlling the mercury vapor pressure in an SEF lamp is to use an alloy capable of absorbing mercury from its gaseous phase in varying amounts, depending upon temperature. Alloys capable of forming amalgams with mercury have been found to be particularly useful. The mercury vapor pressure of such an amalgam at a given temperature is lower than the mercury vapor pressure of pure liquid mercury.
Unfortunately, positioning an amalgam to achieve a mercury vapor pressure in the optimum range in an SEF lamp is difficult. For stable long-term operation, the amalgam should be placed and retained in a relatively cool location with minimal temperature variation. Such an optimal location is at or near the tip, or apex, of the lamp envelope.
Accordingly, it is desirable to provide a relatively simple method and apparatus for introducing and securing an amalgam at or near the apex of the envelope of an electrodeless SEF fluorescent discharge lamp. A practical amalgam support should maintain the optimal location of the amalgam, regardless of lamp orientation.